According to a new study, perturbed skin microbiome can affect the outcome of an infection and also promote inflammation.

Researchers at the University of Pennsylvania have shown for the first time that, not only can infection with the Leishmania parasite alter the skin microbiome of affected mice, but this altered microbial community can be passed to uninfected mice that share a cage with the infected animals.

Mice with the perturbed microbiome, or dysbiosis, had heightened inflammatory responses and more severe disease when they were subsequently infected with Leishmania.

"To my knowledge, this is the first case where anyone has shown that a pre-existing skin microbiome can influence the outcome of an infection or a disease," said Elizabeth Grice, co-senior author and assistant professor in the departments of Dermatology and Microbiology in Penn's Perelman School of Medicine.

In addition, when the researchers examined samples from human Leishmania patients, they found similar patterns of dysbiosis as in the infected mice, a hint that the findings may extend to people.

"The transmission of dysbiosis in the skin from one animal to another is a key finding," said Phillip Scott, professor of immunology in the Department of Pathobiology in Penn's School of Veterinary Medicine and co-senior author on the study.

"And the fact that we saw similar patterns of dysbiosis in humans suggests there could be some very practical implications of our work when it comes to treating people with leishmaniasis," Scott said.

Grice and Scott collaborated with researchers from Penn Medicine and Penn Vet, including lead author Ciara Gimblet, a PhD student in Scott's lab, and colleagues from Brazil's Oswaldo Cruz Foundation.

Cutaneous leishmaniasis is a tropical disease caused by a parasite and transmitted by the bite of a sand fly. The disease results in sores on the skin, which can sometimes become severe and disfiguring. There is no vaccine for the disease and the limited drugs available often fail to provide a complete cure.

Curious about the influence of the skin microbiome on the disease, the Penn-led team swabbed the skin of 44 Leishmania patients, analysing the microbiota not only of their lesions but also the area around them and a portion of skin on the opposite side of the bodies as the lesion.

They noticed that the lesion samples contained less bacterial diversity than the samples of other skin sites. But not all of them were the same; they found three distinct community types: one dominated by Staphylococcus, one by Streptococcus and one that was mixed.